Where in the bible does it say Abraham believed and it was credited to him as righteousness?

The Lord credited Abram's [or Abraham's] believing God as righteousness:-

Gen 15:3 And Abram said, Behold, to me thou hast given no seed: and, lo, one born in my house is mine heir.

Gen 15:4 And, behold, the Word of the LORD came unto him, saying, This shall not be thine heir; but he that shall come forth out of thine own bowels shall be thine heir.

Gen 15:5 And he brought him forth abroad, and said, Look now toward heaven, and tell the stars, if thou be able to number them: and he said unto him, So shall thy seed be.

Gen 15:6 And he believed in the LORD; and he counted it to him for righteousness.

Gal 3:6 Even as Abraham believedGod, and it was accounted to him forrighteousness.